The present invention relates to the testing of echo cancellers used in, for example, telecommunications networks.
Specifically, the invention is directed toward a problem in the testing of echo cancellers used in, for example, telecommunications networks. An echo canceller is typically tested using originating test equipment that transmits a test signal to terminating testing equipment over a path that contains that echo canceller. The originating test equipment measures the residual echo. If the echo canceller is operating properly, the residual echo will be no more than some prescribed amount.
The problem arises when there is at least one additional echo canceller in the path between the originating and terminating test equipment and, additionally, the echo canceller to be tested, referred to herein as the “target” echo canceller, is not the echo canceller closest to the terminating test equipment. The source of the problem is the fact that the other echo canceller(s), referred to as the “tandem” echo canceller(s), will cancel a great deal of the echo before it reaches target echo canceller 12, making it impossible to determine whether the target echo canceller 12 is operating properly.
One possible way to solve this problem is to deploy test equipment at particular points in the field. However, such deployment is, except for the exceptional case, is financially prohibitive.